All of the AA engines work properly and have had batteries inserted. I believe there are 4 or 5 that take C batteries. They MAY work, but I only had 2 Cs to test with that may have been dead. None of the ones requiring Cs had any corrosion (a couple of the AAs did, but still functioned fine) and its obviously possibly user error.
Great starting set of trains for a kiddo. 15 total motorized units I believe in total. 19 cars as well as the case/track.